From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6B5D9388392; Fri, 24 Apr 2026 14:25:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777040749; cv=none; b=LEK7nL9XHxb8kI2qic59Xw8sujeeYjOBkgRpC66pLulpS2Sl6Y1Jdr9fUqTRiQ+sAClrrjsmH61sp5ce6xPOm7Vv9+BxbsHlPVIQqdBF9KgQA/LkSXaz0S4tGg97JTCBignwYhyEWDH8YEkh9bmK5ARx7bn1cgH0NCJrTPd/t/g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777040749; c=relaxed/simple; bh=WgkfmGhCzLmCGzkxUzpe7r47QqHHRuaSNRO9yoR56BQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=gMAX3O6YOhbuyouNw5XWoFnX+2NfYqZlBxbu1/J/4Q3cJSFqUOOq3sk65J3uzN7TCfVTwQwWo7gQWMj8lG2c4JV6cV0Rk4VG2ae3nlusgYHDfEk/PkjX3V5SiG/Qp769Pr9R7Nhqq2TlPuGVRtqYgKK2PkAJJSeD2y5KND89Bu8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DofXVLTZ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="DofXVLTZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AB604C19425; Fri, 24 Apr 2026 14:25:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777040749; bh=WgkfmGhCzLmCGzkxUzpe7r47QqHHRuaSNRO9yoR56BQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=DofXVLTZOLJBasreFFoD4GB529ZJhR9p9hi9FJzzR7k3ya8vwqlS/HZoCOka8sOVP /PiRxL7CrMv6+PHpWjGyPK3rhjRX+R/DAzhh1hBu5Vdlds7d1DNtIsUZ3gaaNJjQzI U3lruPBer07yxkOFicQRfyTZG40sAEGmjBnES58hOCWky276BbHNkvuPG0B/cApuSC sDPcYDMn++TNz+JgIG17HhBOwZlJgpsznHNWxyYqgYE9FYEIOUaOOBwJkYSTeMG6gs ZFkTDa1Ex62JyGwnBDRJ87XhmiVu/CvXRhiS6wA40BHd3G+sBRYaor0qiQFSpGlJxF qnggDM0+yg0NQ== Message-ID: <4b961a07-b72d-4c8a-ab49-23f61ed12b53@kernel.org> Date: Fri, 24 Apr 2026 16:25:41 +0200 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 4/7] mm: add page consistency checker implementation To: Sasha Levin , akpm@linux-foundation.org, corbet@lwn.net Cc: ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, skhan@linuxfoundation.org, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Sasha Levin , Sanif Veeras , "Claude:claude-opus-4-7" References: <20260424140056.2094777-1-sashal@kernel.org> <20260424140056.2094777-5-sashal@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit > + /* > + * Size bitmaps to cover the full PFN range including any holes. > + * Holes waste a few bits but a flat bitmap keeps the indexing > + * trivial (pfn - min_pfn) and avoids additional data structures > + * that would themselves be subject to corruption. This matches > + * the approach used by pageblock_flags. > + */ > + pc_state.min_pfn = PHYS_PFN(memblock_start_of_DRAM()); > + pc_state.max_pfn = PHYS_PFN(memblock_end_of_DRAM()); > + spanned_pfns = pc_state.max_pfn - pc_state.min_pfn; > + if (!spanned_pfns || spanned_pfns > UINT_MAX) { > + pr_err("PFN span %lu cannot be represented by bitmap APIs, feature disabled\n", > + spanned_pfns); > + return; > + } > + > + pc_state.db.nbits = spanned_pfns; > + > + bitmap_bytes = BITS_TO_LONGS(pc_state.db.nbits) * sizeof(unsigned long); > + > + pr_info("Initializing: PFN range [%lu-%lu), %u bits (%zu KB per bitmap)\n", > + pc_state.min_pfn, pc_state.max_pfn, pc_state.db.nbits, > + bitmap_bytes / 1024); > + > + /* Allocate primary bitmap (zeroed by memblock_alloc) */ > + pc_state.db.bitmap[DUAL_BITMAP_PRIMARY] = > + memblock_alloc(bitmap_bytes, SMP_CACHE_BYTES); > + if (!pc_state.db.bitmap[DUAL_BITMAP_PRIMARY]) { > + pr_err("Failed to allocate primary bitmap, feature disabled\n"); > + return; > + } > One bitmap that covers all sparse memory available at boot. Conclusion: Just horrible. -- Cheers, David